1. Field of the Invention
The present invention relates to image forming apparatuses, for use in digital copying machines, laser printers, laser facsimiles, and the like, that form images by what is called as electrophotographic method. More particularly, the invention relates to image forming apparatuses suitable for forming multi-color images.
2. Description of the Related Art
An electrophotographic image forming apparatus for use in a digital copying machine, a laser printer, a laser facsimile, or the like includes a photosensitive element serving as an image carrier and an exposing device for writing image information onto the photosensitive element. An exposing device of this type typically uses a print head that includes a linear light source, such as a light-emitting diode (LED) array or an organic electroluminescence (EL) array, and a rod lens array that guides light emitted from the light source. Example methods for use by the exposing device include, in addition to such a method that uses a print head as discussed above, a laser diode (LD) (semiconductor laser) raster method that uses a semiconductor laser and a polygon scanner; however, in terms of downsizing of apparatus, the method using a print head is more advantageous. Downsizing of laser printers and digital copying machines can be achieved with this method. However, the print head discussed above has a considerably small focal depth of approximately 100 μm; accordingly, a necessity of positioning the print head and a photosensitive element, which is an image carrier, at a given distance from each other with high accuracy arises.
Furthermore, the print head should preferably be located in close proximity of approximately several millimeters to the photosensitive element. This makes a surface of a rod lens array be prone to toner stain. This propensity is particularly pronounced when the LED head is situated upward (in an orientation where light travels upward). Accordingly, to use such a print head, a cleaning mechanism for cleaning the surface of the rod lens array and the like should preferably be used.
The cleaning mechanism for cleaning the surface of the rod lens array and a positioning mechanism for positioning the print head and the photosensitive element, which is the image carrier, at a given distance from each other with high accuracy as discussed above are closely related to each other; hence, it is necessary to deal with these mechanisms linked with each other.
For instance, a configuration for holding a print head and a photosensitive drum, serving as an image carrier, at a given distance from each other by brining a positioning pin projecting from the print head into contact with a periphery of a shaft of the photosensitive drum is disclosed in Japanese Patent Application Laid-open No. 2005-178006 or the like. Such a configuration positions the print head and the photosensitive drum at the given distance from each other with high accuracy.
A configuration that holds a print head and a photosensitive element at a given distance from each other with rollers is disclosed in, for instance, Japanese Patent Application Laid-open No. 2003-39732.
As described above, in Japanese Patent Application Laid-open No. 2005-178006 disclosed is the configuration of holding the print head and the photosensitive drum, which is the image carrier, at a given distance by brining the positioning pin projecting from the print head into contact with the periphery of the shaft of the photosensitive drum. Disclosed in Japanese Patent Application Laid-open No. 2003-39732 is the configuration that holds the print head and the photosensitive element at a given distance from each other with the rollers.
However, with the configuration of Japanese Patent Application Laid-open No. 2005-178006, a surface of a lens array of the print head is to be cleaned by inserting a cleaning member from outside. The positioning pin can be an obstacle interfering with the cleaning member on an insertion path of the cleaning member by, for instance, coming into contact with the positioning pin when the cleaning member is inserted. This can result in failure of insertion of the cleaning member or complicated insertion process. Furthermore, replacement of the photosensitive drum is performed by drawing out the photosensitive drum in a direction parallel to an axial direction of the photosensitive drum (the LED print head is not replaced). While the photosensitive drum is being drawn out, the positioning pin can contact a surface of the photosensitive drum. To avoid this, it is necessary to retract the LED print head by a large amount, which can result in an increase in overall size (due to the large retraction amount) and an increase in complexity of a retracting mechanism.
The configuration of Japanese Patent Application Laid-open No. 2003-39732 is also less preferable in that when the cleaning member is inserted from outside to perform cleaning, the rollers can interfere with the cleaning member, thereby preventing insertion of the cleaning member or making an insertion process complicated.